When a sample is examined through a temperature range in a thermal analyser, one method of exhibiting analytical results is by means of an X-Y recorder where the abscissa is representative of the temperature range through which the sample is subjected. The ordinate then gives an indication of the effect of the temperature on the particular property of the sample under investigation. To view this graphical representation in detail it is advantageous to scale the abscissa such that the temperature range spanned during an experiment is plotted exactly scaled to the pen recorder abscissa such that the left side of the graphical representation corresponds exactly to the minimum temperature reached during the experiment and the right side of the representation corresponds exactly to the maximum temperature reached or anticipated during the experiment. This permits observation of experimental results between the minimum and maximum temperatures of interest as opposed to a range of tempertures over which only a relatively small portion thereof are experimental results desired. Thus, an experimenter who is interested in observing phenomena over a relatively short temperature range may be forced to view the phenomena in a cramped small temperature range within a much larger temperature range represented by the abscissa. Thus, it is highly desirable to be able to select and expand throughout the entire available abscissa that temperature between a minimum temperature and a maximum temperature over which it is desired to observe experimental phenomena.
Heretofore, such adjustments have been done manually which requires that two or more adjustments be made on every occasion that a change is made in the limits between which the sample temperature is to be varied. A signal representative of the sample temperature must be subjected to two operations before being applied to the horizontal input of the pen recorder. An offset of a magnitude equivalent to the minimum temperature that the sample will attain must be subtracted such that when the sample is at this minimum temperature the resultant abscissa drive signal to the pen recorder is zero and the pen is therefore positioned at the left side of the paper. This adjusted signal must then be multiplied by a factor of magnitude equivalent to the full scale signal needed to position the pen recorder along the X axis to the right hand side of the paper divided by the temperature span to which the sample will be subjected. Therefore, the two adjustments necessary are offset and scaling operations. With a manual implementation, the operator must carefully and accurately make these adjustments every time a change of temperature range is made. Since these adjustments may be interactive, a time consuming repetitive procedure may be necessary.
The present invention contemplated apparatus for accurately and automatically making these corrections.